For purposes of convenience, the invention will be described in conjunction with a presently preferred implementation thereof embodied in an electric linear actuator. It will be understood, however, that the principles of the invention may apply equally as well to devices of analogous structure.
The design of automatic floor cleaning equipment often involves a considerable amount of rotary and/or linear motion actuation and control. Positioning of structures such as cleaning heads and squeegees must be accomplished quickly and transparently to the operator. The traditional method of controlling motion on cleaning equipment utilizes limit switches or other proximity switches that either directly control the power to one or more linear actuators, e.g., via relay switches, etc., or indirectly control linear actuators via a signal sent to a CPU indicating the position of the actuators. These switches introduce negative reliability and assembly issues into the design of the machine. For example, an actuator or linkage could be damaged if a jam occurs in mid stroke of the actuator as current would continue to be supplied to the actuator. Additionally, limit switches may become contaminated or damaged through the operation of the machine. The switches may also be mis-aligned during the assembly of the machine. Any of these situations can cause the actuator to stall, overheat, and/or damage the linkage or associated structure coupled thereto.
In mobile equipment systems that include a plurality of electric and or hydraulic devices, such as servo actuators, motors and pumps, it is conventional practice to couple all of such devices to a remote master controller for coordinating or orchestrating device operation to perform a desired task. Motors and actuators may be employed, for example, at several coordinated stages of a surface cleaning machine for automated control of fluids and surface working devices. In accordance with conventional practice, the master controller may comprise a programmable controller or the like coupled to the various remotely-positioned devices. Feedback from the remote devices may be provided via control signals therefrom. For closed-loop operation, a sensor may be coupled to each device for sensing operation thereof, and feeding a corresponding signal to the master controller through an analog-to-digital converter, etc.
Thus, in a system that embodies a plurality of electric and/or hydraulic devices, a substantial quantity of electrical conductors must be provided for feeding individual control signals to the various devices and returning sensor signals to the master controller. Such conductors interfere with system design and operation, and are subject to failure. The bank of D/A and A/D converters for feeding signals to and from the master controller add to the expense and complexity of the overall system. Perhaps most importantly, system performance is limited by capabilities of the master controller. For example, a programmable controller may require one hundred milliseconds to scan a device sensor signal, compute a new control signal and transmit such control signal to the remote device. An overburdened programmable controller may not perform acceptably in high performance applications that may require a ten millisecond response time, for example, at each of a plurality of remote devices.